We have solved the structure of an Alpha-neurotoxin from sea snake venom and refined it to a resolution of 1.38 Angstrom with a crystallographic R-factor currently at 0.21. We shall further refine the structure by means of difference Fourier methods utilizing for the purpose an MMSX molecular graphics system coupled to a VAX computer. The structure led to a theory for the mode of action of the toxin based on invariant residues. Our theory explains the difference between neurotoxins and cardiotoxins. We shall study the latter with a view to obtaining its atomic three dimensional structure. We have purified acetyl-choline receptor and we shall study the association with the neurotoxin with an eventual aim to studying the complex of the neurotoxin with either all or part of the receptor. We are pursuing the structure of thrombin in two ways: molecular replacement based on its homology with chymotrypsin and heavy atom derivatives. The former yeilded a solution to the 'rotation' part but the 'translation' solution still eludes us. The heavy atom work and the search for better crystals of this as well as other clotting factors will be continued.